Nitrogen monoxide and calix[4]pyrrolato aluminate: structural constraint enabled NO dimerization

Area of Science:

• Inorganic Chemistry
• Organometallic Chemistry
• Chemical Catalysis

Background:

• Nitrogen monoxide (NO) dimerization is crucial for biochemical and environmental redox reactions.
• The endergonic nature of NO dimerization presents a significant challenge for broader understanding and control.
• Metal-ligand cooperativity is essential for facilitating challenging chemical transformations.

Purpose of the Study:

• To investigate NO dimerization facilitated by structurally constrained anionic calix[4]pyrrolato aluminate(III) complexes.
• To elucidate the driving forces and mechanisms of N-N bond formation in NO dimerization.
• To explore subsequent redox chemistry, NO decomposition, and ligand rearrangement pathways.

Main Methods:

• Quantum chemical calculations to determine the energetics of N-N bond formation.
• Reactivity tests to study redox chemistry and NO decomposition.
• Kinetic and theoretical studies to analyze ligand rearrangement mechanisms.

Main Results:

• Demonstrated successful NO dimerization using calix[4]pyrrolato aluminate(III) complexes, overcoming the endergonic barrier.
• Identified a key 1,2-adduct intermediate by using nitrosobenzene to inhibit dimerization.
• Observed an unprecedented, high-yielding rearrangement of the calix[4]pyrrolato ligand at elevated temperatures.

Conclusions:

• Structurally constrained aluminum complexes with metal-ligand cooperativity effectively promote NO dimerization.
• The study provides a detailed mechanistic understanding of NO dimerization, redox chemistry, and ligand rearrangement.
• Established a framework for modifying the calix[4]pyrrole macrocycle through ligand rearrangement.